In the ’70s, “Partridge Family” star David Cassidy was the world’s biggest pop star while secretly hating the madness of celebrity. Now Cassidy, 62, gets to experience a different kind of madness — as a murder victim on “CSI” this Wednesday. Cassidy spoke to The Post about “CSI,” and his wild pop-star life.

NYP: You have your throat slit in this episode. What was that like to shoot?

David Cassidy: Extremely messy. Makeup for my face and throat took two hours, and doing the blood was grotesque. Someone who saw the dailies said that it was so vile, they nearly threw up.

How did you like playing a corpse?

The stainless steel was not exactly pleasant.

You were one of the first major teen idols. What do you remember most?

No single person had gone through that kind of madness. The Beatles were the closest. I got to know them, particularly John [Lennon], who was a mentor. In Australia, hundreds of people were passing out [at concerts]. It got so insane. The wisest thing I did was to walk away at the top.

How did you get to know John?

A good friend was doing p.r. for John and Yoko and also for me, and John came to my house on New Year’s Eve, ’73 or ’74. We went into my music room. I sang early Beatles songs with him, and re-taught him a few, because he couldn’t remember them. I told him I wasn’t planning on going back to work [after the tour], and he said, “That’s the best thing you can do for your sanity.”

How did you react when your daughter Katie (Laurel Lance on the CW’s “Arrow”) wanted to be an actress?

She started working in acting class, and said, “I love this.” I said, “Good. If you love the work, just follow that, and you’ll have a career.” And she has, and she’s a very good actress. I’m proud of her.